Laptop Battery Life Calculator: Hours from Wh and Watts
Battery life is capacity divided by power draw. Enter the battery size in Wh and how many watts the laptop uses for your kind of work.
How it works
Runtime in hours equals usable capacity in watt-hours divided by average power draw in watts. A 60 Wh battery feeding a laptop that draws 10 W lasts about 6 hours.
Battery health reduces the usable capacity: a battery at 80% health holds 80% of its design capacity. The usage presets are rough starting points, not measurements. Use a figure from a review of your laptop if you have one.
Questions and answers
How do I find my battery's Wh?
It is printed on the battery or on the bottom of the laptop and listed on the specification sheet. If only mAh and volts are given, multiply them and divide by 1,000.
How many watts does a laptop use?
It varies a lot. Efficient thin laptops can idle at a few watts and browse at well under 10 W, while a gaming laptop under load can draw more than 100 W.
Why is my real battery life shorter than the estimate?
Screen brightness, background apps, battery age and bursts of heavy work all raise the average draw above what you expect.